Did COVID-19 prediction formulas miss something? New study suggests yes

A new study published by an interdisciplinary team of researchers, including several from the University of Florida, suggests prediction models used by decision makers in attempting to control the spread of COVID-19 were incomplete.

“Metapopulations, the Inflationary Effect, and Consequences for Public Health” was published in The American Naturalist.

Led by Robert D. Holt, Ph.D., Arthur R. Marshall, Jr. Chair of Ecological Studies at UF, the study sheds light on how the concept of metapopulations can influence the dynamics of everything from ecosystems to infectious disease spread.

Variability among communities connected by movement, the researchers suggest, were not studied closely enough during the early days of the COVID-19 pandemic and therefore prediction models led to biased results. Given all the factors influencing the spread of the virus, the variability the researchers studied exacerbated the rate of spread.

While the COVID-19 pandemic spread though cities and communities at varying rates, responses were just as varied. For example, despite a relatively low overall infection rate by October 2020, New York State experienced spikes in hospitalizations in the Southern Tier, Hudson Valley and New York City.

Then Governor Andrew Cuomo described the response to this as “COVID whack-a-mole,” as restrictions were localized and control efforts were block-by-block. Such “whack-a-mole” strategies create and maintain variability in space and time that, in principle, allow COVID to spread faster than if the responses were uniform in space. As people traveled, these restrictions were likely less effective in limiting the virus’ spread.

Metapopulations—groups of geographically separated populations linked by movement of individuals from one population to another—are commonly used to compare and predict trends when discussing evolution, ecology, and biology. But when it comes to their use in how disease spreads, the study authors explain, variability through time and across space within a metapopulation can have adverse effects on the outcome.

Climate, social activity, and the fluctuating rate of travel within and between metapopulations can affect their sustainability, and the magnitude of epidemics.

“Because of the complexities in ecological systems, you can have surprises emerge. You can have a system of populations that fluctuates in time, and in a different way, in space,” said Holt. Incorporating these complexities can be difficult, but general lessons can emerge.

“Even if every population has on average a negative local growth rate, suggesting extinction, because of the interplay of movement and variation, the whole metapopulation can persist.”

UF Professor of Geography Gregory Glass, Ph.D., an additional author of the study said, “The people who built the prediction models and gave that information to decision makers, particularly in a pandemic situation, did not take into account the complexity that movement between local populations brings to the calculation.”

The research explains the effect that local events such as disasters or disease outbreaks have on a metapopulation’s survival. However, when measured across multiple local populations, the effects of the local event may be lessened when spread across the larger metapopulation.

During the COVID-19 pandemic, for example, differing policy responses across regions, such as lockdowns, travel restrictions, and varying public health measures, ultimately influenced how the virus spread.

Rather than preventing disease transmission across regions, some of these policies could have inadvertently enhanced it. As people moved from high-infection areas to low-infection areas, they carried the virus with them, leading to a more patchy and dispersed spread of infection. According to researchers, this unintended effect could have been anticipated by a better understanding of metapopulations.

“This paper is an attempt to point out the way that people were thinking about things in terms of how pandemics spread,” Glass said. “They didn’t recognize the qualitative difference that metapopulations put on the models that they had been using all along.”

The study calls for the need for a larger scale perspective. Current models focus a lot on local populations and often fail to capture the intricacies in how metapopulations relate to each other and environmental changes can influence them. To understand what might happen locally, you have to think about what is happening in neighboring locations.